Anodic process for the preparation of tetraalkyl lead compounds

ABSTRACT

An electrochemical process for the anodic alkylation of lead using KAlR2X2 and RX, where R is selected from the group consisting of ethyl, propyl, isopropyl, butyl and isobutyl and X is selected from the group consisting of bromine, chlorine and iodine, with a lead anode and an inert conductor as the cathode.

United States Patent Harwood [54] ANODIC PROCESS FOR THE PREPARATION OF TETRAALKYL LEAD COMPOUNDS [72] Inventor: William H. Hal-wood, Lawton, Okla. 73] Assignee: Continental Oil Company, Ponca City,

Okla.

[22] Filed: Nov. 6, 1969 [2]] Appl. No.: 874,688

[52] US. Cl ..204/59, 204/72 [5 1] Int. Cl ..B0lk 1/00 [58] Field of Search ..204/59 QM [56] References Cited UNITED STATES PATENTS 3,255,224 6/1966 Ziegler et al ..204/59 QM [1 1 3,655,536 [451 Apr. 11, 1972 2,944,948 7/ 1960 Giraitis ..204/59 QM FOREIGN PATENTS OR APPLICATIONS 955,254 4/1964 Great Britain ..204/59 Primary Examiner-John I-I. Mack Assistant Examiner-N. Kaplan Attorney-Joseph C. Kotarski, Henry H. Huth, Jerry B. Peterson, Jack N. Shears and Carroll Palmer [5 7] ABSTRACT An electrochemical process for the anodic alkylation of lead using KAlR X and RX, where R is selected from the group consisting of ethyl, propyl, isopropyl, butyl and isobutyl and X is selected from the group consisting of bromine, chlorine and iodine, with a lead anode and an inert conductor as the cathode.

8 Claims, No Drawings ANODIC PROCESS FOR THE PREPARATION OF 'IETRAALKYL LEAD COMPOUNDS BACKGROUND OF INVENTION 1. Field .of Invention .This invention relates to the preparation of tetraalkyl lead compounds and moreparticularly to an anodic electrochemical process wherein KAIR X in the presence of RX, is reacted at a lead anode to produce tetraalkyl lead compounds.

2. Description of Prior Art There aremany procedures disclosed in the art for the production oforganolead compounds, particularly the commercial product, tetraethyllead. These procedures have all suffered particular disadvantages, among which are the cost and the yield of the organolead product produced. For example, the commercial process used today involves the reaction of .ethyl chloride with a sodium lead alloy. While this process is very efficient, it still sufiers certain inherent disadvantages which desirably are to be overcome. In particular, the maximum conversion of lead possible is one-fourth of the lead employed as reactant with the other three-fourths necessarily being recovered and re-processed.

There have been attempts to provide organolead compounds by electrolytic procedures. For example, Hein et al., Z. Anorg Allgem. Chemie, 141, 161-227 (1924) describes an electrolysis wherein a current is passed through a lead anode into an electrolyte comprising ethyl sodium dissolved in diethylzinc. This procedure operates rather efficiently, but has never been used on a commercial scale for various reasons. For example, inherent in the procedure is the necessity of the difficult preparation of the diethylzinc and ethyl sodium. Further, a disadvantage of the process is that the electrolyte is a highly reactive mixture which is difficult to handle, requiring considerable procaution. Additionally, the conductivity of this system still leaves much to be desired.

An anodic process based upon aluminum triethyl is known; however, while the anodereaction produced tetraethyl lead essentially quantitatively at the anode, the cathode was always subjected to metal deposition which led to objectionable results.

SUMMARY OF INVENTION According to this invention KAlR X is reacted with a lead anode electrochemically in the presence of RX, where R is selected from the group consisting of ethyl, propyl, isopropyl, butyl, and isobutyl and X is selected from the group consisting of bromine, chlorine, and iodine to produce a tetraalkyl lead compound.

DETAILED DESCRIPTION on the lead loss. It was established that a hydrocarbon-soluble lead compound was formed. This was shown by flame photometry to be tetraethyl lead.

The KAlEtgClg was prepared as follows: a powdered KCl sample g) was dried under a vacuum at 150 C. for 24 hours, then placed in the dry box where dry nitrogen was admitted to the evacuated flask. The KCl was then transferred to a 2-liter, three-neck flask, whereupon 200 cc of sodium-dried hexane were added. A glass stirrer was used to keep the flask agitated. A dropwise addition of a room-temperature mixture of 126 cc of AlEt Cl and 126 cc of dried hexane was made using a dropping funnel. After the addition, the hexane was distilled and removed as the product was heated to C. and held at this temperature for 2 hours. Upon cooling, the product crystallized at about 58 C.

The electrical setup was a very simple one which consisted of a DC. power source, a milliammeter, and the electrolytic cell in series. The current used was constant and usually in the order of 20 ma. A simple measurement of the time the current flowed gave us the number of coulombs and, from that, the number of electrical equivalents used in the experiment. Comparisons could then be made with the equivalents of lead lost from the anode, or the equivalents of aluminum gained by the cathode. For low temperatures, a glass cell was used. At temperatures greater than 20 C., due to the higher vapor pressure of ethyl chloride, a small stainless steel bomb of 250-cm capacity was utilized. In some experiments, the vapor pressure of ethyl chloride reached psi. The bomb was fitted with removable electrodes which were led in by packing seals capable of holding 1,000-psi pressure. A glass liner with a dividing glass-fritted membrane was used inside the bomb to hold the sample.

After electrolysis, the sample and the electrolyte were removed from the cell. In some cases, the sample was further extracted with pentane to recover hydrocarbon-soluble lead compounds. The electrodes were then washed, first with hexane and finally with acetone, and reweighed to determine their 'gain or loss in weight. The amount of hydrocarbon-soluble lead material was determined by flame photometry.

While the exact electrode processes of this system are not known, it is believed that the following reactions take place:

- and at the cathode:

4e- 4/3 AiEtrClr 4/3 A1 8/3 Et- 8/3 01- tollowed by 4/3 Al 2EtCl 2/3AIE122C1 2/3A1Et01;

At the temperatures used, 70 90 C., the groups attached to the aluminum atom are very labile, and the AlEtCl could, under these conditions, decompose to give A1Et C1 and AlCl Therefore, the total over-all reaction could be given as:

Pb KAlEtgClg 2EtCl PbEt, AlCl KC].

Table 1 shows the results of several experiments using the concepts of this invention.

TABLE 1 A. Electrolysis oi KAlEtzClg and ethyl chloride Composition of Equivalents electrolyte (cc.) of aluminum Equivalents of Electrical deposited at lead lost at equivalents Sample number KA1(Cl H Cl O H Cl CathodeX10 anodeXlO used 90 10 Nil 203 174 D0 10 N11 90 20 2 618 637 90 20 Nil 580 595 90 30 Nil 401 410 90 30 3 832 373 90 40 N11 375 385 90 40 Nil 380 395 90 None 225 220 230 90 None 235 228 242 B A hydrocarbon-soluble Electrolytic conditions:

Suitable compounds for use in this invention are those having the formula KAlRgxg and RX where R is selected from the group consisting of ethyl, propyl, isopropyl, butyl and isobutyl, and X is selected from the group consisting of bromine, chlorine and iodine. The preferred materials are KALEt,Cl= and EtCl. The RX compound should be present in the range of about -30 wt. percent, based on the KAIR,X, compound.

Suitable cathode materials are those metals which are inert to the system, such as, for example, platinum, nickel and titanium.

While the system can operate without a solvent, certain solvents, such as N,N-dimethylformamide, acetonitrile and N- methyl pyrrolidone, are useful in that they decrease the vapor pressure and help stabilize the product.

The reaction should be carried out at a temperature range of about 60 to about 105 C., with a preferred temperature of about 70 C.

Pressure of the system will vary depending upon the temperature and the amount of RX present, with the preferred pressure being about 60 psi.

Having thus described the invention by providing specific examples thereof, it is to be understood that no undue restrictions of limitations are to be drawn by reason thereof and that many modifications and variations are within the scope of the invention.

compound at the anode and withdrawing said tetraalkyl lead compound from the electrolyte.

2. The process of claim 1 wherein said electrolyte consists essentially of KAlEgCl, and BC].

3. The process of claim 1 wherein said cathode is a metal selected from the group consisting of platinum, nickel and titanium.

4. The process of claim 1 wherein the reaction is carried out in a solvent selected from the group consisting of N,N- dimethylformamide, acetonitrile and N-methyl pyrrolidone.

5. The process of claim 1 wherein said RCl compound is present in the range of 10 to 30 wt. percent based on the KAIR X compound.

6. The process of claim 1 wherein said reaction is carried out at a temperature between about 60 C. and about C.

7. The process of claim 1 wherein said reaction is carried out at about 70 C.

8. The process of claim 1 wherein said KAIR CI is prepared by reacting KC] with AIR CL 

2. The process of claim 1 wherein said electrolyte consists essentially of KAlEt2Cl2 and EtCl.
 3. The process of claim 1 wherein said cathode is a metal selected from the group consisting of platinum, nickel and titanium.
 4. The process of claim 1 wherein the reaction is carried out in a solvent selected from the group consisting of N,N-dimethylformamide, acetonitrile and N-methyl pyrrolidone.
 5. The process of claim 1 wherein said RCl compound is present in the range of 10 to 30 wt. percent based on the KAlR2X2 compound.
 6. The process of claim 1 wherein said reaction is carried out at a temperature between about 60* C. and about 105* C.
 7. The process of claim 1 wherein said reaction is carried out at about 70* C.
 8. The process of claim 1 wherein said KAlR2Cl2 is prepared by reacting KCl with AlR2Cl. 